Raised photodiode sensor to increase fill factor and quantum efficiency in scaled pixels

Abstract

An image pixel cell with a doped, hydrogenated amorphous silicon photosensor, raised above the surface of a substrate is provided. Methods of forming the raised photosensor are also disclosed. Raising the photosensor increases the fill factor and the quantum efficiency of the pixel cell. Utilizing hydrogenated amorphous silicon decreases the leakage and barrier problems of conventional photosensors, thereby increasing the quantum efficiency of the pixel cell. Moreover, the doping of the photodiode with inert implants like fluorine or deuterium further decreases leakage of charge carriers and mitigates undesirable hysteresis effects.

1. An imager comprising:
 a substrate having a first surface level; 
 an array of pixel cells formed partially in said substrate, at least one pixel cell of said array comprising:
 a first photosensor structure formed in said substrate, said first photosensor structure including a first doped region extending to said first surface level; and 
 a second photosensor structure formed above said first surface level, said second photosensor structure comprising an epitaxial material formed on said first surface level, and a first hydrogenated amorphous silicon material formed on said epitaxial material. 
 
 
     
     
       2. The imager of  claim 1 , wherein said epitaxial material and said first hydrogenated amorphous silicon material have opposite doping types. 
     
     
       3. The imager of  claim 2 , wherein said first hydrogenated amorphous silicon material is doped n-type, and said epitaxial material is doped p-type. 
     
     
       4. The imager of  claim 1 , wherein said epitaxial material is located adjacent a transfer transistor. 
     
     
       5. The imager of  claim 4 , wherein said epitaxial material is in contact with an oxided sidewall of said transfer transistor. 
     
     
       6. The imager of  claim 1 , wherein each photosensor further comprises a second hydrogenated amorphous silicon material formed over said first hydrogenated amorphous silicon material. 
     
     
       7. The imager of  claim 6 , wherein at least one of said first and second hydrogenated amorphous silicon materials further comprises fluorine. 
     
     
       8. The imager of  claim 6 , wherein at least one of said first and second hydrogenated amorphous silicon materials further comprises deuterium. 
     
     
       9. The imager of  claim 1 , wherein said pixel cells of said array are CMOS cells. 
     
     
       10. The imager of  claim 1 , wherein said at least one pixel has a fill factor of at least fifty percent. 
     
     
       11. The imager of  claim 2 , wherein said first hydrogenated amorphous silicon material is doped p-type, and said epitaxial material is doped n-type. 
     
     
       12. The imager of  claim 1 , wherein said first and second photosensor structures generate charge carriers in response to applied light. 
     
     
       13. The imager of  claim 1 , wherein said first photosensor structure is one of a pnp, npn, np, and pn photodiode. 
     
     
       14. The imager of  claim 1 , said at least one pixel cell further comprising an insulation region surrounding said second photosensor structure. 
     
     
       15. An imager comprising:
 a substrate having a first surface level; 
 an array of pixel cells formed partially in said substrate, at least one pixel cell of said array comprising:
 a first photosensor structure formed within said substrate; 
 a second photosensor structure formed above said first surface level, said second photosensor structure having an epitaxial region formed on said substrate and a first hydrogenated amorphous silicon region formed on said epitaxial region; and 
 an insulation region surrounding said second photosensor structure. 
 
 
     
     
       16. The imager of  claim 15 , said at least one pixel cell further comprising at least one transistor formed in said substrate, wherein at least a portion of said first photosensor structure extends horizontally above the at least one transistor. 
     
     
       17. The imager of  claim 15 , wherein said first hydrogenated amorphous silicon material further comprises fluorine. 
     
     
       18. The imager of  claim 15 , wherein said first hydrogenated amorphous silicon material comprises deuterated amorphous silicon. 
     
     
       19. The imager of  claim 15 , wherein said at least one pixel cell has a fill factor greater than fifty percent. 
     
     
       20. The imager of  claim 15 , wherein said imager is a CMOS imager. 
     
     
       21. The imager of  claim 15 , wherein said imager is a component in a processor system, said processor system further comprising:
 a processor coupled to said imager. 
 
     
     
       22. The imager of  claim 15 , said second photosensor structure further comprising a second hydrogenated amorphous silicon region formed on said first hydrogenated silicon region. 
     
     
       23. The imager of  claim 22 , said epitaxial region extending to a second surface level and said second hydrogenated amorphous silicon regions extending to a third surface level, wherein said insulation region extends from said second surface level to said third surface level. 
     
     
       24. The imager of  claim 23 , wherein said insulation region extends from said first surface level to said third surface level. 
     
     
       25. The imager of  claim 15 , said first photosensor structure including a first doped region extending to said first surface level.